A resin anchored rock bolt with a locating formation at a leading end

ABSTRACT

Disclosed is a centralising positioner for a resin bolt which includes a central attachment part which is adapted to engage a leading end of the bolt and a positioning part integral with the attachment part that extends from the attachment part.

BACKGROUND OF THE INVENTION

This invention relates to a rock bolt for use in a resin anchoredapplication.

It is well known in the art to anchor a rock bolt into a rock hole witha grout or a two-part resin. The grout or resin is introduced into therock hole, ahead of the bolt, by means of grout or resin capsules.

The rock bolt has to be adapted to puncture the capsule to release thecontents. With the two-part resin, the contents have to be thoroughlymixed to achieve optimal setting.

Strictly, the resin is not an adhesive as it does not adhere the rockbolt to the rock hole. The resin mechanically locks the rock bolt in therock hole. Thus, there is a reliance upon mechanical interlock withirregularities in the surface of the rock bolt and the rock hole wallsto prevent the rock bolt from being pulled from the rock hole. Theirregularities on the surface of the rock bolt are provided by aprofiled surface.

Another factor influencing optimal mechanical lock is how efficient therock bolt is at mixing the two parts of the resin. Typically mixingefficiency decreases in a radial direction from the surface of the rockbolt to the rock hole wall. This means that the larger the ratio betweenthe diameter of rock hole and the rock bolt, i.e. the larger the annularspace between the rock bolt and the rock hole wall, the greater themixing inefficiency towards an outer circumference of the annular space.Potentially, this reduces the load bearing capacity of the rock bolt.

This factor places a limit on the diametric size of the rock bolt thatcan be used for a particular hole size. There is economic motive tousing as small a rock bolt as possible.

A resin rock bolt therefore must have features which are a compromisebetween a mixing and an anchoring function. Unfortunately, the functionsare not complementary. Optimising the mixing features tends to decreasethe anchoring abilities of the bolt. A typical rock grouted resinanchored rock bolt is profiled with a series of ridges angled at 45°.These ridges provide a compromise between anchoring and mixingfunctionality.

Gloving is another problem in resin bolting. This phenomenon occurs whenthe plastic wall of the capsule is incompletely broken up or disruptedby the rock bolt when the bolt penetrates the capsule. The plastic thencoats part of the rock bolt, covering the profiled surfaces of the rockbolt and decreasing its anchoring and mixing functionality.

Yet another issue in resin bolting is that the rock bolt is very rarelyinserted in complete co-axial alignment with the rock hole causingeccentricity of the bolt to the rock hole, about the distal end of thebolt. At the distal end, the annular space is irregular, with a thin anda thick annular arc. In the thin annular arc there is insufficient resinto provide optimal mechanical interlock. Whilst in the thick annulararc, the resin is insufficiently mixed. And with insufficient resin inthe small annular arc, the protective barrier provided by the resin isthinned, increasing the chance of acid mine water penetrating to therock bolt.

Both eccentricity and gloving tends to occur in the critical top of theleading end section of the installed bolt.

The invention aims, at least partly, to address the aforementionedproblems.

SUMMARY OF THE INVENTION

The invention provides a centralising positioner for a resin bolt whichincludes a central attachment part which is adapted to engage a leadingend of the bolt and a positioning part integral with the attachment partthat extends from the attachment part.

The attachment part may be a disc-shaped part.

The positioning part may be a circumscribing umbrella formationextending from a perimeter of the attachment part.

The umbrella formation may be biased in an open or flared position andis resiliently movable from the open position to a closed or foldedposition.

The unitary umbrella formation may be made of a sheet material which isperforated with a plurality of resin flow-through holes.

Alternatively, the positioning part may comprise a plurality of locatingfingers integral with and projecting from a perimeter of the attachmentpart.

The fingers may extend backwardly in a first direction which is aslantto a plane of the attachment part.

The locating fingers may be evenly radially spaced about the perimeterand have equal lateral reach.

Preferably, the positioner has three or four locating fingers.

The positioner may be forged from a slug or blank metal or moulded usinga rigid plastics material.

The positioner may have a penetrating formation upstanding from theplane of the attachment part in a second direction which is opposed tothe first direction.

The penetrating formation may be comprised of a radial grouping oftriangular, orthogonal or rectangular sections, or the like, bent awayfrom the plane of the central attachment part.

Alternatively, the attachment part may have a central aperture forreceiving a peaked formation on the leading end of the bolt.

The invention extends to a resin anchored rock bolt which has anelongate metal body which extends between a leading end and a trailingend and at least one centralising positioner which has a centralattachment part which is adapted to engage the leading end of the boltand a positioning part integral with the attachment part that extendsfrom the attachment part in even lateral extent.

The attachment part may be a disc-shaped part.

The positioning part may be a circumscribing umbrella formationextending from a perimeter of the attachment part.

The unitary umbrella part may be perforated with a plurality of resinflow-through holes.

Alternatively, the positioning part may comprise a plurality of locatingfingers integral with and projecting from a perimeter of the attachmentpart.

The positioning part may extend in a first direction which is aslant toa plane of the attachment part.

The locating fingers may be evenly radially spaced about the perimeter.

Preferably, the positioner has three or four locating fingers.

The positioner may be made punched from a blank of flat stock steel ormoulded using a rigid plastics material.

The positioner may have a penetrating formation upstanding from theplane of the attachment part.

The penetrating formation may be comprised of a radial grouping oftriangular, rectangular or orthogonal sections, or the like, bent awayfrom the plane of the central part.

Alternatively, the leading end of the rock bolt is conically shaped andthe attachment part may have a central aperture for receiving theconical leading end.

In an alternative to the single centralising positioner described above,the rock bolt may include at least two centralising positioners; a firstpin and a second pin and a leading end of the rock bolt may be formedwith a first formation and a second bore formed diametrically through aleading end portion of the body, wherein the first formation isorthogonal to the second bore and wherein the first pin and second pinare adapted to engage the first formation and second bores respectivelywith projecting parts of each pin evenly laterally extending from thebolt body.

The first formation may be a groove formed diametrically across theleading end. Alternatively the first formation may be a first boreformed diametrically through the leading end portion.

The pins may engage the first formation and the second bore in frictionfit.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is further described by way of example with reference tothe accompanying drawings in which:

FIG. 1 is a partial view in elevation of a resin anchored rock with acentralising positioner bolt in accordance with the one embodiment ofthe invention;

FIG. 2 is an isometric view of a penetrating end of the resin bolt ofFIG. 1;

FIG. 3 is a view in plan onto the penetrating end of the rock bolt;

FIG. 4 is an isometric view of a centralising positioner in accordancewith a second embodiment of the invention, with a penetrating formationas part of the positioner; and

FIG. 5 diagrammatically illustrates a centralising positioner inaccordance with a third embodiment engaged with a penetrating end of aresin anchored rock bolt of the invention;

FIG. 6 diagrammatically illustrates a resin anchored rock bolt with acentralising positioner in accordance with a fourth embodiment of theinvention; and

FIG. 7 diagrammatically illustrates a resin anchored rock bolt with acentralising positioner in accordance with a fifth embodiment of theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 of the accompanying drawings illustrates a leading end portion ofa resin bolt 10 which is in accordance with the invention. The resinbolt has an elongate solid steel shaft 12 which extends between aleading end 14 and a trailing end (not shown).

The shaft of the resin bolt 10 in this example is of typical manufacturewith a series of profiled ridges 18 formed in an outer surface of theshaft. And, in this particular embodiment, the resin bolt has a paddleformation 20 which is integrally formed of the body. The paddle not onlyincreases the diametric reach of the resin bolt in mixing the resincontent of pre-installed resin capsules (not shown) but also increasethe anchoring of the bolt within the rock hole.

To the leading end 14, a centralizing positioner 22 is attached by anysuitable means, for example by tack welding. The centralizing positioner22 is illustrated in greater detail in FIGS. 2 and 3. The centralizingpositioner 22 can be made, punched from a blank of flat stock steel oralternatively moulded using a suitable rigid plastics material. What isdescribed hereafter is a positioner made of flat stock steel.

The centralizing positioner 22 has a core ring 24 and a plurality oflocating fingers, respectively designated 26A, 26B and 26C, integralwith and projecting from a perimeter 28 of the core ring 24. In thisexample, there are three locating fingers which have lateral extension,so that an outer surface 30 of each finger can abut against a wall of arock hole in use, as will be more fully described below, but which benddownwardly towards the trailing end of the bolt 10 so as to not toresist passage of the resin bolt 10 as it is inserted into the rock holein use.

The locating fingers 26 are evenly radially spaced about the perimeterand are laterally co-extensive so as to keep a leading end of the boltrelatively concentric with the hole during insertion.

In the embodiment illustrated, the core ring 24 has a central aperture32 which locates over a conical formation 34 on the leading end 14 ofthe rock bolt 10, before being welded in place. The conical formation 34not only locates the centralising positioner 18, it also functions topuncture the frangible wall of pre-installed resin capsules.

In another embodiment, illustrated in FIG. 4, where the resin bolt 10does not have the conical formation 34, the puncturing function can beprovided by a penetrating formation 36 on the positioner 22A itself.

As illustrated, the penetrating formation 36 is comprised of a pluralityof triangular sections 38 which are centrally grouped on the core ring24. Each of the sections, which are provided by making a “+” shaped cutin the ring 24, is bent upwardly about a respective base to project fromthe plane of the ring 24. The bend angle of each section is uniformensuring that the sections taper towards one another to a peak 40.

In a further embodiment, illustrated in FIG. 5, a centralisingpositioner 22B is provided. The positioner includes a resin capsulelocating formation 50 and an umbrella formation 52 which radiates from,and which is pivotally connected about a circumferential connecting line54 to, the formation 50. The locating formation has a base 56 and acircumferential wall 58 that is upstanding from the base. The base has ahole 60.

The umbrella formation 52 is comprised of a single sheet of suitableplastics or polymeric material. Radiating through the formation, fromline 54, are a number of fold lines 62 dividing the umbrella formationinto a number of segments 64.

A plurality of apertures (not shown) can be formed through the sheet ofthe umbrella formation to allow passage of grout from a grout capsuleside 66 of the formation to an underside 68.

As illustrated in FIG. 5, the upstanding cupula provider within thecylindrical wall 58 within which a resin capsule 70 can be inserted andresiliently held therein prior to insertion into a rock hole ahead ofthe rock bolt.

The umbrella formation 52 extends, in a relaxed biased state, to definea circumferential maximum. However in use as will be more fullydescribed below, the umbrella formation can move resiliently inwardly,relatively to the resin capsule locating formation 50, to acircumferential minimum by folding or buckling about the fold lines 62.

With the resin capsule engaged with the formation 50, the device can beinserted into a rock hole. As the umbrella formation 52, which ismaximally flared prior to insertion, reaches the mouth of the rock hole,it will be forced inwardly by contact with the mouth of the hole into afolded or partially folded state and resiliently held in that foldedstate by contact with the rock hole walls. With the umbrella formation54 accommodating ingress in this manner, the resin capsule 70 can bepushed up towards a blind end of the hole, with the resin capsule 66leading.

The resin bolt 10 trails the resin capsule locating formation 50 ininsertion into the rock hole. During insertion, a leading end 14 of thebolt will dock with the formation from an underside. A conical orpenetrating formation (34 or 36) will penetrate through the hole 60 inthe base 56 to contact and puncture the retained resin capsule 70.

Having a resin bolt that is centralised, during insertion, and a resincapsule that is held in the hole, in a concentric position, will ensurethat the resin capsule is optimally positioned to be punctured and notto fall away from the bolt into the annular space. The umbrellaformation 52 also ensures that the plastic packaging of the capsule isseparated from the rock bolt so not as to glove about the bolt.

Once punctured, the grout contents are released to flow downwardly whereit will optimally adhere the bolt to the rock walls because of annularregularity provided by the centralising positioner (22 or 22B).

FIGS. 6 and 7 illustrate another two embodiments of the invention. Inboth embodiments, the centralising positioner comprises a pair of pins(respectively designated 70A and 70B), either cylindrical or rectangularin shape, engaged with a leading end 14 of the resin bolt 10.

In the embodiment of FIG. 6, the leading end of the bolt is formed witha groove 72 which diametrically extends across the end. The groovereceives a first pin 70A, either in frictional fit or fixed by anysuitable means. Below the end, a second bore 76 is formed through aleading end portion 78 of the bolt. The bore extends diametricallythrough the body in a direction which is orthogonal to the groove 72.This orthogonal relationship is illustrated in FIG. 6A and 7A. Thesecond pin 70B engages with this bore, again either in friction fit orfixed therein by any suitable means.

In the embodiment of FIG. 7, the groove 72 is replaced with a first bore72B. The first pin 70A is received through the first bore.

The laterally extending end portions of each pin 80 are each of uniformlength so as to position the resin bolt centrally within the rock holewhen inserted.

1. A centralising positioner for a resin bolt which includes a centralattachment part which is adapted to engage a leading end of the bolt anda positioning part integral with the attachment part that laterallyextends from the attachment part.
 2. A centralising positioner accordingto claim 1 wherein the positioning part is a circumscribing umbrellaformation which extends from a perimeter of the attachment part.
 3. Acentralising positioner according to claim 2 wherein the umbrellaformation is biased in an open or flared position and is resilientlymoveable from the open position to a closed or folded position.
 4. Acentralising positioner according to claim 2 wherein the umbrellaformation is made of a sheet material which perforated with a pluralityof resin flow-through holes.
 5. A centralising positioner according toclaim 1 wherein the positioning part is comprised of a plurality oflocating fingers integral with and projecting from a perimeter of theattachment part.
 6. A centralising positioner according to claim 5wherein the locating fingers are evenly radially spaced about theperimeter and each have equal lateral reach.
 7. A centralisingpositioner according to claim 5 wherein the positioner has three or fourlocating fingers.
 8. A centralising positioner according to claim 5wherein the fingers extend in a first direction which is aslant to aplane of the attachment part.
 9. A centralising positioner according toclaim 8 which has a penetrating formation upstanding from the plane ofthe attachment part in a second direction which is opposed to the firstdirection.
 10. A centralising positioner according to claim 9 whereinthe penetrating formation is comprised of a radial grouping oftriangular or orthogonal sections bent away from the plane of thecentral attachment.
 11. A centralising positioner according to claim 1wherein the attachment part has a central aperture for receiving apeaked formation on a leading end of the bolt.
 12. A resin anchored rockbolt which has an elongate metal body which extends between a leadingend and a trailing end and at least one centralising positioneraccording to claim
 1. 13. A resin bolt according to claim 12 wherein thepositioner has a penetrating formation upstanding from the plane of theattachment part.
 14. A resin bolt according to claim 13 wherein thepenetrating formation is comprised of a radial grouping of triangular ororthogonal sections bent away from the plane of the central attachment.15. A resin bolt according to claim 12 wherein the leading end of therock bolt is conically shaped and the attachment part has a centralaperture for receiving the conically shaped leading end.
 16. Acentralising positioner according to claim 3, wherein the umbrellaformation is made of a sheet material which perforated with a pluralityof resin flow-through holes.
 17. A centralising positioner according toclaim 6, wherein the positioner has three or four locating fingers. 18.A centralising positioner according to claim 6, wherein the fingersextend in a first direction which is aslant to a plane of the attachmentpart.
 19. A centralising positioner according to claim 7, wherein thefingers extend in a first direction which is aslant to a plane of theattachment part.
 20. A centralising positioner according to claim 2,wherein the attachment part has a central aperture for receiving apeaked formation on a leading end of the bolt.